The numerical control system of a machine tool must, on the one hand, read out numerous sensors (e.g., position measurement units) and, on the other hand be able to supply actuators (such as axial drives) with commands. If the sensors and actuators are addressed via a common interface, a large number of such peripheral units can become established. In this context, various registers may occur within one peripheral unit. Thus, the most various different data are offered by one position measuring unit, such as various voltage levels of the position sensors (e.g., for the phase-shifted scanning of a grating structure) or information on the type of the position sensor.
German Patent No. 43 42 052 describes a control computer which is connected to several peripheral units via an address bus. In order to be able to address the peripheral units, a device is described using which the peripheral units are able to be assigned an address, simply and free of error.
The problem may arise that, for safety-directed applications, which occur ever more frequently in the field of numerical control of machine tools, correct functioning of the interface between the numerical control system and the peripheral units must be assured. It may be important that the peripheral units should not be mixed up. If several peripheral units of the same construction are present, the reading out of a register having identifications specific to type of construction is not sufficient, because these identifications are the same for all peripheral units of the same construction. However, if a wrong peripheral unit is addressed, which is, however, of the same construction as the one that was actually intended, a position value is, for example, read out of a register which is not able to be at once recognized by the control as being nonsensical, since it does correspond to a position value, however, as it happens, of the wrong peripheral unit. Such a mistake may take place if the address bus of the interface between the numerical control system and the peripheral unit works faultily.
Thus, in the case of a defect of the interface between control and peripheral unit, even given error-free specification of the addresses in the peripheral units, according to German Patent No. 43 42 052, exchange mistakes may be made with respect to the peripheral units.
In safety-directed numerical control systems, it is also conventional to record critical parameters (such as position values) with the aid of sensors designed in duplicate, which are scanned via two separate interfaces. However, it may be very expensive to implement such interfaces in duplicate. It may be more favorable to secure the function of a single interface such that both sensors may be scanned without there being a danger of mixing up the two sensors.
It is an aspect of the present invention to provide a method with the use of which the interface between a numerical control system and its peripheral units may be checked in a simple manner.